Field of the Invention
The invention relates to a process for the safe operation of a printing machine. The printing machine has a first cylinder driven by a first motor and a second cylinder driven by a second motor and the first cylinder accepts sheets of paper from the second cylinder or delivers them to the latter by a gripper system. Furthermore, the invention relates to a printing machine for the execution of the process. The printing machine has a first cylinder with a gripper system, a first motor for driving the first cylinder, a second cylinder, and a second motor for driving the second cylinder.
The invention results from the following background: sheet-fed printing machines contain cylinders with gripper systems for holding the sheets of paper. Some sheet-fed printing machines contain cylinders that are adjoining one another and are coupled to one another mechanically by a pair of toothed wheels such that the cylinders can be driven by a common motor. The pair of toothed wheels provides the cylinders with a positive coupling so as to ensure that the cylinders run synchronously with each other in all circumstances and to eliminate the possibility of a collision of a gripper system of one cylinder with the other cylinder.
However, there are also sheet-fed printing machines in which the cylinders do not have any such pair of toothed wheels and that are driven by different motors. As long as the motors work in a trouble-free manner, the synchronous motion of the cylinders is ensured and thus the possibility of a collision of the gripper system is eliminated. In order to avoid such a collision even in case of a malfunction of one of the motors or the malfunction of its control, additional precautionary measures are necessary.
These precautionary measures includes, for instance, in providing the safety device described in published, non-prosecuted German patent application DE 42 02 722 A1 (corresponding to U.S. Pat. No. 5,365,841). However, the process according to which this safety device works is not suitable for every printing machine.
A further prior art reference, published, non-prosecuted German patent application DE 199 09 686 A1 describes a device for controlling the grippers, wherein the grippers are swiveled below the periphery of an impression cylinder in order to be able to perform maintenance work.